An organic light emitting phenomenon means a phenomenon for converting electric energy into light energy by using an organic material. That is, when an appropriate organic material layer is disposed between an anode and a cathode, if a voltage is applied between two electrodes, a hole is injected into the organic material layer at the anode, and an electron is injected into the organic material layer at the cathode. When the injected hole and electron meet each other, exciton is formed, and light is emitted when the exciton falls to the bottom state again.
In recent years, researches to manufacture displays or light sources by using organic light emission have been actively performed. In addition, in order to manufacture an effective organic light emitting device, a study for depositing an organic material layer from a single layer to a multilayered structure has been made. Most organic light emitting devices that are currently used have a structure in which an electrode and an organic material layer are planarily deposited, and among them, as shown in FIG. 1, an organic light emitting device that has a multilayered structure in which an organic material layer 3 including multilayers such as a hole injection layer, a hole transfer layer, a light emitting layer on a substrate 1 and an electron transfer layer and electrodes 2 and 4 are planarily deposited are used as the most representative device. In the application of the organic light emitting device, an increase in light emission efficiency has a very important meaning in respects to competition to another technology. In the case of a flat display, in addition to issue in respects to high-quality image, it is seriously competitive in conjunction with LCD in terms of power consumption, and lighting is competitive in conjunction with LED (light emitting diode) in terms of light emission efficiency.
If electrons and holes are injected into an organic light emitting device by applying voltages to the organic light emitting device having a planar structure, they are recombined with each other in the light emitting layer to emit light. At this time, light that is generated in the light emitting layer may travel through the following different two paths by a difference in refractive index in each layer. That is, there are a case of when light is emitted to the outside of the device, and a case of when total reflection occurs at the interface between the transparent substrate and the air layer or at the interface between the transparent substrate and the transparent electrode, such that light is confined in the device (FIG. 2). At this time, the quantity of light that is capable of being emitted to the outside of the device is 1/2n2 or less (n is the refractive index of the organic material layer) of light that is generated in the light emitting layer. If the refractive index of the organic material layer is 1.7, about 17% or less of generated light may be emitted to the outside of the organic light emitting device.
By the more detailed analysis, the total reflection does not exist only at the interface between the transparent substrate and the air layer, but it is known that the total reflection frequently occurs at the interface between the transparent electrode having the relatively higher refractive index than that of the transparent substrate and the transparent substrate. In general, the refractive index of the glass substrate is in the range of 1.5 to 1.6, but in the case of the ITO (indium tin oxide) that is the transparent anode commonly frequently used, since the refractive index is in the range of 1.8 to 2.1, the total reflection occurs at the interface between the glass substrate and the transparent anode. The angle at which the total reflection starts to occur is referred to as a critical angle of the total reflection, and the angle may be represented by the equation relating to the refractive index at the interface between the adjacent two layers, that is, θC=sin−1 (n2/n1). Herein, n2 is a media having the relatively low refractive index, and n1 is a media having the relatively high refractive index.
In order to emit light in a more quantity to the outside of the organic light emitting device while the above problems are overcome, an effort for manufacturing an organic light emitting device that has a structure including a layer that is not flat unlike the organic light emitting device as shown in FIG. 1, that is, a non-planar structure has been made. However, a structure that is capable of significantly improving light emission efficiency has not yet been developed.